Integrate web_template design system and fix security/quality issues

Security fixes:
- Add HTTP method validation to delete_comment.php (block CSRF via GET)
- Remove $_GET fallback in comment deletion (was CSRF bypass vector)
- Guard session_start() with session_status() check across API files
- Escape json_encode() data attributes with htmlspecialchars in views
- Escape inline APP_TIMEZONE config values in DashboardView/TicketView
- Validate timezone param against DateTimeZone::listIdentifiers() in index.php
- Remove Database::escape() (was using real_escape_string, not safe)
- Fix AttachmentModel hardcoded connection; inject via constructor

Backend fixes:
- Fix CommentModel bind_param type for ticket_id (s→i)
- Fix buildCommentThread orphan parent guard
- Fix StatsModel JOIN→LEFT JOIN so unassigned tickets aren't excluded
- Add ticket ID validation in BulkOperationsModel before implode()
- Add duplicate key retry in TicketModel::createTicket() for race conditions
- Wrap SavedFiltersModel default filter changes in transactions
- Add null result guards in WorkflowModel query methods

Frontend JS:
- Rewrite toast.js as lt.toast shim (base.js dependency)
- Delegate escapeHtml() to lt.escHtml()
- Rewrite keyboard-shortcuts.js using lt.keys.on()
- Migrate settings.js to lt.api.* and lt.modal.open/close()
- Migrate advanced-search.js to lt.api.* and lt.modal.open/close()
- Migrate dashboard.js fetch calls to lt.api.*; update all dynamic
  modals (bulk ops, quick actions, confirm/input) to lt-modal structure
- Migrate ticket.js fetchMentionUsers to lt.api.get()
- Remove console.log/error/warn calls from JS files

Views:
- Add /web_template/base.css and base.js to all 10 view files
- Call lt.keys.initDefaults() in DashboardView, TicketView, admin views
- Migrate all modal HTML from settings-modal/settings-content to
  lt-modal-overlay/lt-modal/lt-modal-header/lt-modal-body/lt-modal-footer
- Replace style="display:none" with aria-hidden="true" on all modals
- Replace modal open/close style.display with lt.modal.open/close()
- Update modal buttons to lt-btn lt-btn-primary/lt-btn-ghost classes
- Remove manual ESC keydown handlers (replaced by lt.keys.initDefaults)
- Fix unescaped timezone values in TicketView inline script

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/delete_comment.php

@@ -21,8 +21,19 @@ try {
     require_once dirname(__DIR__) . '/models/TicketModel.php';
     require_once dirname(__DIR__) . '/models/AuditLogModel.php';
 
+    // Only allow POST or DELETE — reject GET to prevent CSRF bypass
+    $method = $_SERVER['REQUEST_METHOD'];
+    if ($method !== 'POST' && $method !== 'DELETE') {
+        http_response_code(405);
+        header('Content-Type: application/json');
+        echo json_encode(['success' => false, 'error' => 'Method not allowed']);
+        exit;
+    }
+
     // Check authentication via session
-    session_start();
+    if (session_status() === PHP_SESSION_NONE) {
+        session_start();
+    }
     if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
         throw new Exception("Authentication required");
     }
@@ -48,9 +59,9 @@ try {
     $data = json_decode(file_get_contents('php://input'), true);
 
     if (!$data || !isset($data['comment_id'])) {
-        // Try query params
-        if (isset($_GET['comment_id'])) {
-            $data = ['comment_id' => $_GET['comment_id']];
+        // Also check POST params (no GET fallback — prevents CSRF bypass via URL)
+        if (isset($_POST['comment_id'])) {
+            $data = ['comment_id' => $_POST['comment_id']];
         } else {
             throw new Exception("Missing required field: comment_id");
         }